Ablation catheter with cooled linear electrode

ABSTRACT

The ablation catheter is comprised of a guiding catheter and an inner catheter. The guiding catheter is comprised of a shaft section which is attached to an articulating section at its distal end and a first handle at its proximal end. The inner catheter is comprised of an elongated central shaft, an electrode assembly attached to the distal end of the central shaft, and a second handle attached to the proximal end of the central shaft. The electrode assembly is comprised of a flexible plastic catheter tube having an outer surface, a porous tip electrode, and at least one linear electrode carried on the outer surface of the catheter tube. The electrode assembly is articulated to better align the electrode assembly to the generally arcuate shape of the inner chambers of the heart.

FIELD OF THE INVENTION

This invention relates generally to a cardiac catheter used forperforming cardiovascular procedures on the heart. More particularly,this invention relates to an ablation catheter used predominantly fortreating cardiac arrhythmias.

BACKGROUND OF THE INVENTION

Radio frequency ablation (RFA) has become a common treatment fortreating specific cardiac arrhythmias. Portions of the heart sometimesform alternative conduction pathways which interfere with the normalconduction of the electrical signals which regulate the beating of theheart thereby causing some cardiac arrhythmias to occur. In order toremove these alternative conduction pathways, the heart is first mappedthrough catheter mapping procedures in order to find where thesealternative conduction pathways are located, and then RFA is used toprevent these areas of the heart from disrupting the normal conductionpatterns of the heart.

RFA typically involves the use of a specialized ablation catheter whichis positioned at the site of the alternative conduction pathway. Radiofrequency (RF) waves are then typically delivered through the ablationcatheter and onto the alternative conduction pathway. The radiofrequency waves create heat at the site of the alternative conductionpathway creating a lesion which destroys the tissues forming thealternative conduction pathways.

Ablation catheters have been developed in order to deliver radiofrequency waves at the site of the abnormal pathway. While some of theseprior art ablation catheters are well suited for particular procedures,the ability of these prior art ablation catheters to perform a varietyof procedures effectively have been limited due to a number structuralconstraints which are necessitated by the spatial and physiologicalrequirements of the applications in which these ablation catheters areto be used. Size, flexibility, and maneuverability are common restraintswhich have previously prevented more effective ablation catheterdesigns.

One drawback to the prior art is their inability to make a variety oflesions. There are typically two types of lesions which are generated byablation catheters. One type of lesion is a focal lesion where the RFwave is concentrated at a point. Typically, the prior art is limited tomaking focal lesions. A tip electrode carried on the distal tip of anablation catheter is preferably used for making focal lesions. However,there are a variety of procedures in which linear lesions are preferred,requiring that the RF energy be delivered along a line. There are priorart ablation catheters which are capable of creating linear lesions;however, these prior art ablation catheters are not particularly suitedfor making focal lesions. A linear electrode is preferably utilized formaking linear lesions. Although tip electrodes can also be used utilizedfor making linear lesions, the use of tip electrodes to make linearlesions can be significantly more difficult and time consuming.

The maneuverability of the prior art ablation catheters also limit theireffectiveness. The ablation catheters are typically utilized within theinterior chambers of the heart. The precise placement of the electrodesonto the site to which the RF waves are to be delivered and thesufficiency of the contact between an electrode and the sitesignificantly impacts the effectiveness of the treatment. Linearelectrodes, and especially longer linear electrodes, tend to be stiffer,making it more difficult for them to maneuver and to conform to thegenerally arcuate shape of the interior walls of the heart.

Another problem common amongst the prior art ablation catheters is theformation of coagulum around the electrode during ablation. The heatgenerated by the RFA sometimes causes the electrode to overheat causingthe blood surrounding the electrode to coagulate on the electrode. Asthe coagulum collects on the electrode, the impedance between theelectrode and the site to which the RF wave is applied increases therebyreducing the effectiveness of the electrode. As a result it is oftennecessary to stop the RFA in order to remove the coagulum from theelectrode.

Accordingly, it is an object of this invention to provide an ablationcatheter which is capable of generating both focal lesions and linearlesions while having the appropriate size, flexibility andmaneuverability to enable it to be used effectively in a variety of RFAprocedures.

Accordingly, it is also an object of this invention to provide for anablation catheter with a linear electrode which is easily maneuverableand conforms readily to the arcuate shape of the interior of the heartwhile still having the appropriate size, flexibility and maneuverabilityto enable the ablation catheter to be used effectively in a variety ofRFA procedures.

Accordingly, it is also a further object of this invention to provide anablation catheter with a means for cooling the the electrode in order toreduce the rate at which the coagulum builds up on the surface of anelectrode while still having the appropriate size, flexibility andmaneuverability to enable it to be used effectively in most RFAprocedures.

Other objects and advantages of the invention will become apparent asthe description proceeds.

To achieve these objectives, and in accordance with the purposes of thepresent invention the following ablation catheter is presented. As willbe described in greater detail hereinafter, the present inventionprovides the aforementioned and employs a number of novel features thatrender it highly advantageous over the prior art.

SUMMARY OF THE INVENTION

In accordance with an illustrative embodiment of the present invention,an ablation catheter is provided which comprises two major components,an articulating guiding catheter and an inner articulating catheterdisposed therein. The guiding catheter is typically inserted into thevascular system and is guided and manipulated through the vascularsystem until it reaches the appropriate chamber of the heart. The innercatheter is disposed within the guiding catheter until a desiredlocation in the heart is reached. At that point the inner catheter isthen extended beyond the guiding catheter allowing the inner catheter tomore precisely position itself onto a treatment site.

In an illustrative embodiment, the guiding catheter is comprised of ashaft section which is attached to an articulating section at its distalend and a first handle at its proximal end. The inner catheter iscomprised of an elongated central shaft, an electrode assembly attachedto the distal end of the central shaft, and a second handle attached tothe proximal end of the central shaft.

In one embodiment, the electrode assembly is comprised of a flexibleplastic catheter tube having an outer surface, a porous tip electrode,and at least one linear electrode carried on the outer surface of thecatheter tube. The catheter tube is used to provide axial and radialstability to the electrode assembly and to provide a conduit to theelectrode assembly. Fluid is distributed to the linear electrode and theporous tip electrode through a plurality of apertures extending from theinner surface of the catheter tube to the outer surface of the cathetertube.

The linear electrode is utilized in order to make linear lesions in theheart tissue. In one embodiment, the linear electrode is comprised of atubular array of conductive metal strands carried on the outer surfaceof the catheter tube, the conductive strands extending along thecatheter tube in a plurality of directions relative to the longitudinalaxis of the catheter tube. In one embodiment, the tubular array of metalstrands is a wound helical coil. In an alternate embodiment, the tubulararray of metal strands is arranged in a braided construction. The poroustip electrode is located at the distal end of the electrode assembly.The tip electrode provides a means for creating lesions concentrated atparticular points in the heart, otherwise called focal lesions.

Articulation of the electrode assembly is utilized in order to betteralign the linear electrode to the generally arcuate shape of the innerchambers of the heart. One means for articulating the electrode assemblyis by extending a pull wire through the inner catheter and attaching itto the distal tip of the catheter tube. An alternate means forarticulating the electrode assembly is achieved by running the pull wirethrough the inner catheter then having the wire run externally along thelinear electrode and then finally attaching the pull wire to the distaltip of the electrode assembly. A second alternate means for articulatingthe electrode assembly is achieved through the use of a memory shapedtube which is thermally activated to conform to a predetermined shapeupon reaching body temperature.

A more detailed explanation of the invention is provided in thefollowing description and claims, and is illustrated in the accompanyingdrawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a planar view of an ablation catheter embodying features inaccordance with the present invention.

FIG. 2 is a side section view of the distal portion of the ablationcatheter shown in FIG. 1 providing an enlarged view of the electrodeassembly.

FIG. 3 is a side view of a linear electrode assembly having helicallywound coils.

FIG. 4 is a side view of a linear electrode assembly having a braidedconstruction.

FIG. 5 is a side section view of a linear electrode assembly utilizingcoils made of hypodermic tubing.

FIG. 6 is a side section view of a linear electrode assembly utilizingcoils made of a combination of hypodermic tubing and solid wire.

FIG. 7 is a side section view of a linear electrode assembly with addedmonitoring capabilities.

FIG. 8 is side section view of a linear electrode assembly having anarticulating means.

FIG. 9 is a side section view of a linear electrode assembly having anexterior articulating means.

FIG. 10 is side section view of a linear electrode assembly having athermally activated alternative articulating means.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Referring to FIG. 1, an ablation catheter is comprised of two majorcomponents, an articulating guiding catheter 10 and an innerarticulating catheter 50 disposed therein. The guiding catheter 10 istypically inserted into the vascular system and is guided andmanipulated through the vascular system until it reaches the appropriatechamber of the heart. Once positioned within the heart, the guidingcatheter 10 provides a uniform conduit for introducing the innercatheter 50 into the chambers of the heart. The inner catheter 50 isdisposed within the guiding catheter and typically travels within theguiding catheter until a desired location in the heart is reached. Atthat point the inner catheter 50 is then extended beyond the guidingcatheter 10 allowing the inner catheter 50 to more precisely positionitself onto a treatment site.

The guiding catheter 10 is comprised of a shaft section 12 having anarticulating section 19 at its distal end and a first handle 14 attachedat its proximal end. A plurality of ring electrodes 13 is carried on thedistal end of the guiding catheter 10. The ring electrodes 13, when incontact with the heart tissue, are able to take measurements ofendocardial potentials. The shaft 12 is comprised of preferablyconstructed of an inner and outer layer of plastic which encapsulate abraided metal but other means of constructing the shaft would worksuitably with the present invention. The handle 14 is comprised of afirst mechanism for articulating 17 the articulating section 19, aninterface for electricity 15, a first fluid interface 16, and aninterface for inserting 18 the inner articulating catheter 50. It shouldbe understood that various additional interfaces can be incorporated inthe guiding catheter.

The inner catheter 50 is comprised of an elongated central shaft 53, anelectrode assembly 54 attached to to the distal end of the centralshaft, and a second handle 56 attached to the proximal end of thecentral shaft 53. The inner catheter is removably disposed within theguiding catheter, allowing the inner catheter to be removed andreinserted into the guiding catheter a number of times during a medicalprocedure.

The second handle 56 is comprised of a second mechanism 55 forarticulating the distal end of the inner catheter 50, an RF interface 58for connecting the inner catheter 50 to an RF generator, and a secondfluid inter face 57. The second fluid interface is connected to aseparate lumen within the inner catheter that extends to the distal endof the inner catheter, providing a conduit for fluids from the secondfluid interface to the electrode assembly 54. It should also beunderstood that various additional interfaces can be incorporated in theinner catheter design.

Referring to FIG. 2, the electrode assembly 54 is comprised of aflexible plastic catheter tube 60 having an outer surface, a porous tipelectrode 52 attached on the outer surface at the distal end of thecatheter tube 60, and at least one linear electrode 61 carried on theouter surface of the catheter tube 60.

The catheter tube 60 is used to provide axial and radial stability tothe electrode assembly and to provide a conduit for the flow of fluid tocool the linear electrode 61 and tip electrode 52. The catheter tube 60is preferably a thin walled, non conductive, single lumen tubeconstructed of a flexible polymer plastic. Fluid received from thesecond fluid interface flows through the inner catheter 50 to thecatheter tube 60. There the fluid is distributed to the linear electrode61 and the tip electrode 52 through a plurality of apertures 62extending from the inner surface of the catheter tube 60 to the outersurface of the catheter tube 60. The apertures 62 are spaced to allowfor uniform flow of fluid to all parts of the linear electrode 61 andthe porous tip electrode 52. During a RFA procedure, “hot spots” maydevelop on sections of an electrode if there is not enough fluid flowreaching the area. Since fluid is being uniformly delivered to allsections of the linear electrode 61 and tip electrode 52 through thecatheter tube 60, the chances for a “hot spot” to develop is minimizedor eliminated.

The linear electrode 61 is utilized in order to make linear lesions inthe heart tissue. The linear electrode can be attached either to theelongated central shaft 53 or the catheter tube 60. Conductive wireconnect the linear electrode to the RF interface 58. The linearelectrode 61 is comprised of a tubular array of conductive metal strandscarried on the outer surface of the catheter tube 60, the conductivestrands extending along the catheter tube 60 in a plurality ofdirections relative to the longitudinal axis of the catheter tube 60.The conductive strands are preferably made from rounded or flat solidwire 311 or hypodermic tubing 300 or a combination of both as shown inFIGS. 5 and 6. Hypodermic tubing has the advantage of enabling thelinear electrode 61 to be cooled by circulating fluid within thehypodermic tubing as well as from fluid flow from the apertures 62 inthe catheter tube 60.

Referring to FIG. 3, in one embodiment, the tubular array of metalstrands is a wound helical coil 200. The spacing between loops in thecoil is varied in order to achieve different physiological effects. Theloops can be wound tightly with each loop in the coil in contact withits neighboring loops as in FIG. 3 or the loops can be wound loosely asin FIG. 5. A tight spacing of the loops in the coil will enable thelinear electrode 61 to deliver a higher energy density, but may increasethe stiffness of the linear electrode and may increase parasitic powerloss. Greater spacing between the loops in the coil will provide moreflexibility and less power loss. Referring to FIG. 4 in an alternateembodiment, the tubular array of metal strands is arranged in a braidedconstruction 201.

Referring to FIG. 7, in order to add more precise electrocardiac mappingcapability, additional monitoring electrodes 401 can be placed onto thelinear electrode 61. The monitoring electrodes would preferably rest onan insulating sleeve 402 electrically isolated from the linearelectrode. The monitoring electrodes are preferably cylindrical metallicbands 401. The metallic bands 401 are coupled to physiologicalmonitoring equipment through a wire 403 extending from the metallic bandand through the inner catheter.

Referring to FIG. 2, the porous tip electrode 52 is located at thedistal end of the electrode assembly 54. The porous tip electrode 52provides the inner catheter 50 a means for creating lesions concentratedat particular points in the heart, otherwise called focal lesions. RFenergy is supplied to the porous tip electrode through a conductor wire65 which extends from the tip electrode 52 to the RF interface 58 in thesecond handle 56.

Referring to FIG. 8, articulation of the electrode assembly is utilizedin order to better align the linear electrode 51 to the generallyarcuate shape of the inner chambers of the heart. One means forarticulating the electrode assembly is by extending a pull wire 501 fromthe second mechanism for articulating 55 through the inner catheter 50and attaching it to the distal tip of the catheter tube 60. Creating apulling motion on the pull wire 501 by means of the second mechanism forarticulating 55 will cause the distal end of the catheter tube 60 todeflect towards the direction of the pulling motion. A stiffener can beused in this configuration in order to return the electrode assembly 54back to its original position. Referring to FIG. 9, an alternate meansfor articulating the electrode assembly is achieved by running the pullwire 501 from the second mechanism for articulating 55 through the innercatheter 50, then having the wire run externally along the linearelectrode and then finally attaching the pull wire 501 to the distal tipof the electrode assembly 54.

Referring to FIG. 10, a second alternate means for articulating theelectrode assembly is achieved through the use of a memory shaped tube702 which is thermally activated to conform to a predetermined shape.Nitinol™ tubing or other materials having thermally activated shapememory characteristics can be used for the catheter tube 60. Thecatheter tube would remain relatively erectile during the positioning ofthe electrode assembly 54, but once the RF energy is applied, thethermal energy would cause the Nitinol™ tubing to deflect into anarcuate shape. This means for articulation has the advantage of notrequiring the use of pull wires 501 or mechanisms for articulating.

It can be seen that the ablation catheter which has been provided aboveallows for greater choice in the type of lesions which can be made, alsoallows for greater maneuverability, more precise placement, and bettercooling of the electrodes. Although illustrative embodiments of theinvention have been shown and described, it is not intended that thenovel device be limited thereby. It is to be understood that this novelinvention may be susceptible to modifications and variations that arewithin the scope and fair meaning of the accompanying claims anddrawings.

What is claimed:
 1. A catheter which comprises: an elongated, centralshaft having a lumen and a distal end; and an electrode assemblyattached to said elongated central shaft, said electrode assemblycomprising a tubular array of one or more conductive metal strandsdefining apertures extending between said strands, to constitute alinear electrode, and a device for articulating said electrode assembly,said catheter having a plurality of cooling fluid flow paths that extendfrom said lumen laterally though said apertures of the tubular array ofstrands and to the catheter exterior.
 2. The catheter of claim 1 furthercomprising a porous tip electrode located on a distal end of saidcatheter tube.
 3. The catheter tube of claim 1 wherein the strands ofsaid linear electrode are made from tubing which allows cooling fluid toflow therein.
 4. The catheter tube of claim 1 wherein said linearelectrode is a helical coil of said strands.
 5. The catheter tube ofclaim 1 wherein said linear electrode is of a braided strandconstruction.
 6. The catheter tube of claim 1 wherein the articulatingdevice comprises at least one pull wire attached to a distal end of saidelectrode assembly.
 7. The catheter tube of claim 1 wherein saidcatheter tube is made from Nitinol™ tubing thereby allowing saidcatheter tube to bend to a predetermined shape upon the application ofradio frequency energy.
 8. The catheter of claim 1 further comprisingmonitoring electrodes nonconductively mounted on said linear electrode.9. The catheter of claim 1 in which said electrode assembly is attachedat one end to an end of said elongated, central shaft, other portions ofsaid electrode assembly being spaced from said elongated, central shaft.10. The catheter of claim 1 in which said electrode assembly surroundssaid elongated, central shaft.
 11. The catheter of claim 1 in which saidelectrode assembly is laterally exposed to the exterior of saidcatheter.
 12. A catheter that carries a linear electrode, which cathetercomprises: a flexible plastic catheter tube having a lumen and an outersurface; and at least one linear electrode comprising a tubular array ofconductive metal strands carried on the outer surface of the cathetertube, said conductive strands extending along said catheter tube in aplurality of directions relative to the longitudinal axis of thecatheter tube, to define said linear electrode, said catheter having aplurality of fluid of cooling fluid flow paths that extend from saidlumen laterally through said tubular array of conductive strands and tothe catheter exterior.
 13. The catheter of claim 12 in which saidelectrode assembly is attached at one end to an end of said cathetertube, other portions of said electrode assembly being spaced from saidcatheter tube.
 14. The catheter of claim 12 in which said electrodeassembly surrounds said catheter tube.
 15. The catheter of claim 14 inwhich said catheter tube defines a plurality of apertures to permit theflow of cooling fluid from the lumen of said catheter tube and throughsaid apertures, to flow among said conductive metal strands.
 16. Thecatheter of claim 14 in which said conductive metal strands are inbraided configuration.
 17. The catheter of claim 14 in which saidconductive metal strands respectively extend generally helically instrand-crossing relation with other helical strands of said tubulararray.
 18. The catheter of claim 14 in which at least some of saidconductive metal strands are tubular, and are connected to a source ofcooling fluid for fluid flow there through.
 19. The catheter of claim 14which carries a catheter steering mechanism.
 20. The catheter of claim14, positioned within a lumen of an outer guiding catheter for assistingcatheter delivery to a desired location within the body of a patient,said guiding catheter having a second catheter steering system.
 21. Acatheter that carries a linear electrode, which catheter comprises: aflexible plastic catheter tube having a lumen; and at least one linearelectrode comprising a tubular array of conductive metal strands carriedby said catheter tube, said conductive strands extending along saidcatheter tube in a plurality of directions relative to the longitudinalaxis of said catheter tube, to define said linear electrode, saidcatheter having a plurality of fluid of cooling fluid flow paths thatextend from said lumen laterally through said tubular array ofconductive metal strands and to the catheter exterior.
 22. The catheterof claim 21 in which said conductive metal strands are in a braidedconfiguration.
 23. The catheter of claim 21 in which said conductivemetal strands comprise a conductive metal tube having a wall with atleast about half of the wall area removed to form apertures.
 24. Thecatheter of claim 21 in which said tubular array of conductive metalstrands is bonded at one end to the catheter tube, most of the remainderof said tubular array being longitudinally spaced from the cathetertube.
 25. The catheter of claim 21 in which said conductive metalstrands respectively extend generally helically in strand-crossingrelation with other helical strands of said tubular array.
 26. Thecatheter of claim 21 in which at least some of said conductive metalstrands are tubular, and are connected to a source of cooling fluid forfluid flow there through.
 27. The catheter of claim 21 which carries acatheter steering mechanism.
 28. The catheter of claim 21 positionedwithin a lumen of an outer guiding catheter for assisting catheterdelivery to a desired location within the body of a patient, saidguiding catheter having a second catheter steering system.
 29. Acatheter which comprises: a flexible plastic catheter tube having anouter surface; and at least one ablation electrode comprising a tubulararray of conductive metal strands carried by the catheter tube, saidtubular array carrying at least one sensing electrode, and wiresseparately connecting said ablation and sensing electrodes to a controland power source.
 30. The catheter of claim 29 in which said tubulararray comprises braided metal strands.
 31. The catheter of claim 29 inwhich said tubular array connects at one end to an end of said cathetertube.
 32. The catheter of claim 29 which carries a catheter steeringmechanism.
 33. The catheter of claim 12 in which said electrode assemblyis laterally exposed to the exterior of said catheter.
 34. A catheterthat carries a linear electrode, which catheter comprises: a flexibleplastic catheter tube; and at least one linear electrode comprising atubular array of conductive metal strands carried by said catheter tube,said conductive strands extending along said catheter tube in aplurality of directions relative to the longitudinal axis of saidcatheter tube, to define said linear electrode, said catheter beingpositioned within a lumen of an outer guiding catheter for assistingcatheter delivery to a desired location within the body of a patient,said guiding catheter having a catheter steering system.
 35. Thecatheter of claim 21 in which said electrode assembly is attached at oneend to an end of said catheter tube, other portions of said electrodeassembly being spaced from said catheter tube.
 36. The catheter of claim21 in which said electrode assembly surrounds said catheter tube. 37.The catheter of claim 21 in which electrode assembly is laterallyexposed to the exterior of said catheter.
 38. A catheter whichcomprises: an elongated central shaft having a distal end; and anelectrode assembly attached to the distal end of said elongated, centralshaft, said electrode assembly comprised of a catheter tube having aplurality of apertures therethrough, a linear electrode, and a devicefor articulating the electrode assembly, said catheter furthercomprising monitoring electrodes nonconductively mounted on said linearelectrode.
 39. A catheter that carries a linear electrode, whichcatheter comprises: a flexible plastic catheter tube having an outersurface; and at least one linear electrode comprising a tubular array ofconductive metal strands carried on the outer surface of the cathetertube, said conductive strands extending along said catheter tube in aplurality of directions relative to the longitudinal axis of saidcatheter tube, to define said linear electrode, said catheter beingpositioned within a lumen of an outer guiding catheter for assistingcatheter delivery to a desired location within the body of a patient,said guiding catheter having a catheter steering system.
 40. A catheterthat carries a linear electrode, which catheter comprises: a flexibleplastic catheter tube; and at least one linear electrode comprising atubular array of conductive metal strands carried by said catheter tube,said conductive strands extending along the catheter tube in a pluralityof directions relative to the longitudinal axis of said catheter tube,to define said linear electrode, said conductive metal strandscomprising a conductive metal tube having a wall with at least abouthalf of the wall area removed to form apertures.